1. Field of the Invention
The present invention relates to internal combustion engines. More particularly, the present invention relates to a cylinder head for an internal combustion engine, in which the cylinder head has an improved intake port configuration, and to an engine incorporating the improved cylinder head.
2. Background Art
The intake ports of internal combustion engines are formed in the cylinder head of the engine. Each intake port consists of a passage which leads from an inlet side, at an upstream end thereof, through the cylinder head and to an opening of a combustion chamber. During engine operation, intake air is guided into the combustion chamber through the intake ports. An intake valve, which opens and closes the intake opening of the combustion chamber, has a valve stem extending perpendicularly from the center of the opening. In order to minimize the effect of the presence of the valve stem, the intake port extends upwardly and outwardly, in a curved shape, from the intake opening of the combustion chamber.
A valve guide is, therefore, fixed to a curved wall formed in the cylinder head. The curved wall is located on a side of the cylinder head which is spaced away from a center of curvature of the intake port. The intake valve is freely slidably supported by the valve guide.
Thus, in a common intake port configuration, an intake port extends from an upstream end, at an upper side of the cylinder head, to a downstream end at an opening of a combustion chamber. The valve guide is situated at a location in the intake port such that the valve stem is substantially aligned with a central vertical axis of the intake port. Such a configuration is disclosed, for example, JP-A No. 301119/1995.
In common cases, the portion downstream of the location of the valve guide of an intake port leads to an opening of a combustion chamber with almost no change in passage cross-sectional area.
Therefore, in this conventional design, the intake air flowing into the intake port is, after flowing curvedly along a curved wall surface, led perpendicularly to the intake opening of the combustion chamber as it is, without being caused to spread or being compressed. Most of the intake air then directed toward a circular end portion of an intake valve. In this arrangement, the intake air entering the combustion chamber is subjected to a large resistance so that it is difficult to improve the efficiency of intake into the combustion chamber.
The present invention has been made in view of the above problem, and it is an object of the present invention to provide cylinder head having an improved intake port configuration including an improved intake port passage configuration, to allow intake air to flow into a combustion chamber more efficiently than with previously known cylinder head designs.